Classification



March 15, 1938. A. J. WEINIG 2,111,082

CLASSIFICATION 1 Original Filed April 9, 1932 NEW MILL FEED FIG.

DISCHARGE OVER 25 FIN/SHED FINES PLUS FRACflO/V omen/e050 FRACTION OF$11 545 OF SLIME /4 ZSnventor a ARTHUR JOHN WE/NIG attorney Patented15,1938

UNITED STATES alum crass s'rcs'rrom' Arthur John Welnir, Golden, com. mmto The Stearns-ItogerOmDm-, ver',Colo.,andTheDsrr0ssnpany,!nc.,New

York, N. Y.

Original application a. less, seem a...

April 604,151, now Patent No. 2,101,109, dated Januapplication Dividedall!- this liiarch s, 1931. Serial No. 129.191

2 mum. (cl. sea-4oz) This patent matures from a patent applicationcarved from my parent patentapplication Serial No. 604,151, filed April9, i932, patented January 4, 1938, No. 2,104,709. It is thought that 5 areader hereof will be helped to a quicker understanding of the inventionclaimed herein as compared to the invention claimed in the parent case,by the following remarks that are in the nature of a prologue.

The invention of the said parent patent application was described, forthe purposes of illustration, as being used in a'closed-circuit grindingsystem comprising a grinding mill, a primary classification stage, and asecondary classification stage.

A quantity of one of the productsof the secondary classification stagewas described as having two advantageous uses. One use was by beingsupplied to the grinding mill, and the second use was by being suppliedto the classifier bath in the classification stage. It became apparentduring the time that the said patent application was being prosecuted,that there was disclosed therein a multiplicity of inventions. The firstinvention related to improvements in closed-circuit grinding or ingrinding-mill circuits; the second invention related to improvements inmethods of classification claimed in my copending application Serial No.'74,833,-fl1ed April 17, 1936; and the third to improvements inclassifier apparatus.

The present case is drawn'to the feature, namely, improvements inclassification apparatus, and resides in the provision of 'means wherebythe density of the classifier bath is 30 increased. j

In the parent case, from which there have been carved out two divisionalcases drawn to the above-mentioned second and third in'ventlonsrespectively, of which this case covers the 9 third, there is adisclosure of the desirability of supplying a grinding mill with solidmaterial in colloidal form, that is, material whose particle size has adiameter that causes the material to act as a colloid; in other words,to have a tendency to remain in suspension.

Such colloidal material has a novel and unexpected eil'ect in thegrinding mill. It has also been found to have a novel and unexpectedeffeet when supplied to the classifier bath or pool.

50 So this invention is directed to a classifier apparatus havingProvision for supplying to the pool or bath thereof colloidalmaterialjor material having its particles of colloidal size for thepurpose'of increasing the density of the classifier 55 bath, by virtueoi which'greater selectivity of 4 on may be obtained by classifiers ofpresent-day general types, irrespective of whether or not they are usedin a grinding-mill circuit. This feature of advantage will be found andde scribed with more particularity in the latter part 5 of the followingspecification.

This finishes the prologue, so there now follows the main body of thespecification, copied from parts of said parent patent application.

This invention revolves about the setting up 10 and maintaining in thegrinding device, a condition of plasto-lubrlcity which is brought aboutin a simple manner by feeding to the grinding mill, slime having certaincharacteristics, the chief of which is that it shall contain as many aspossible 16 of colloidal-like particles. In theory these particlesshould be of the diameter of a micron or less, but in practice I aim touse particles having a diameter up to and including that of a suspensoidwhich sometimes is called a suspen- 20 sion. An ideal concurrentcondition would be to have the slime substantially free of particlesbetween a micron and oversize, but this is not possible in commercialoperating conditions, so I approach this condition as nearly as possible25 under operating conditions. This slime may be added to the mill as aseparate substance, such as bentonlte. However, in tests with closedcircult grinding, it has been shown that in grinding practicsllyeverysubstance capable of such treat- 30 ment, the grinding operationautomatically produees slime, some portion of which, contains thedesired size of particles. 80 under all normal conditions, no extraneousmaterial is likely to be needed to get the required slime conditions, atleast after they have been. first built up within the s d ns circuit.

But one feature of the required slime condition is that there-be addedto the mill, a minimum of unfavorablv sized particles or grains between40 those of a micron in size and those which are of the desired mesh forwhich grinding is being done. For example, suppose we are grinding toget s48 mesh product. There will be in the mill solids ranging frommolecular size to those up to suspensoldic size. Let us call that rangeA. 'lhen there will be other solids fallingln a range which will becalled 13 including sizes from suspensoidic to say 65 mesh. There willalso be'solids of +65 +48 mesh, which will be called 50 C. And thoselarger than .48 mesh, or oversize, will be called D. It is those in therange .3 that this invention teaches should NOT be recirculated to themill, for they are already small enoush so the mill should not beburdened with 56 them. It is the quantity thereof which should be keptdown to aminimum. It is the grains in the range A which I refer to asthe favorable fraction of slime that I want to have continually presentin the mill. Those in the range C constitute the finished mill product,while those in the range D must be recirculated to the mill for furthergrinding.

This invention therefore, also contemplates the separating orselectingout from the mill discharge, solids in various size ranges whereby thosein range C are removed from the circuit and are ready for some type ofsubsequent treatment; those in range 3 are removed from the circuit andjoin those in range C as finished product, while those in ranges D and anecessary portion of those in range A are recirculated through the millalong with the new mill feed. So a most important point of thisinvention lies in recirculating to the system, or through the mill,slime having colloidal types of solids within size limits up to asuspensoid as well as oversize, while eliminating as far as possiblefrom the mill return all other fines or slime.

I have accompanied this specification with a drawing for illustrativepurposes. In'the drawing, Figure 1 shows diagrammatically the manher inwhich the mill discharge is subdivided andtreated, Figure 2 showsdiagrammatically how a balanced condition is set up in the secondaryclassifierY.

In a simple application, the invention may be carried out in a grindingmill circuited with a classifier. The mill discharge is fed to a primaryclassifier; This classifier separates out the oversize which is returnedto the mill and the overfiow from the classifier contains the desiredfines plus slime. This overflow is then exposed to further separation orselection such as by classification or hydroseparation where thedesirable fines plus the fraction of slime unfavorable to grinding aredischarged at the sand end of the classifier and the fraction of slimefavorable to grinding is recovered from the slime end of the classifier.

This favorable fraction preferably is returned to the mill forrecirculation therethrough. The discharge from the secondaryclassification or separation contains the other or unfavorable fractionof the slime plus the end product sands and some portion of thefavorable fraction of slimes, the mixture of which form the finishedproduct of the circuit. As will be shown later, my invention providessimple means for controlling a proportion of the favorable slimes in thesystem, which are eliminated from the system with the finished material,and of keeping the amount of slimes so eliminated equal to the amount ofslimes produced in the mill.

But in practice, it is not as easy to do as might appear. Certainconditions must be caused to exist in the classifying stages in order toobtain the precise selectivity required.

Referring to Fig. l, and to the fiowsheet shown therein, the new millfeed, enters the ball mill and so does the circulating load. The milldischarge is composed, as usual, of oversize, fines and slime.classification stage or classifier X. This classifier makes twoseparations. The oversize sands are separated and discharged by theclassifier from whence. they are returned to the mill as circulatingload. The separated overfiow from this classifier contains the finesplus the slime The discharge goes to a primary produced by grinding inthe mill and what slime is circulating in the system.

This overflow from the classifier X, composed of fines and slime, isthenfed to a secondary classification or other separation stage such asa classifier Y. In this classifier, thetwo portions or fractions ofslime are selectively separated, the unfavorable fraction of which withthe finished fines are discharged and are ready for use. The favorablefraction of slime may preferably be overfiowed from classifier Y into acompartment or reservoir Z from whence it goes to recirculation to theball mill or classifier, or to both. The unfavorable fraction, composedof the larger sized slime solids are thus discarded or eliminated fromthe circuit and thus are precluded from getting back into the mill. Theyare ejected or rejected from the system or circuit by being mixed withthe finished fines and exit with them.

The circulation through the mill of this favorable fraction of slimeproduces the various desirable conditions in the ball mill hereinbeforereferred to and which I term plasto-lubricity. That is, the individualgrains in. the mill adhere to and coat the balls and yet the balls andthe mass of sands are mobile and cascade freely independently of eachother.

Referring now to the classifier X, greater selectivity is required thanis ordinary. This can be accomplished in various ways. I propose now tomake certain modifications of the classifier. One constitutes increasingthe density of the classifier bath in order to refine the selectivity orefiiciency of classification of the classifier. This increase of densityof classifier bath may be done in any suitable manner, although mypreferred plan is to return to the classifier bath some of the favorablefraction of slime. The favorable fraction of slime tends to have aconstant density. In one ore treated, the density of the recirculatedfraction of slime was maintained fairly constantly at 1.23, but ofcourse this can be varied to meet the requirements of difier- -ent oresor materials being ground or to meet different conditions in grindingthe same material.

The reason for this increased density of classifier bath is to endeavorto preclude the passing to discharge of any undesirable larger particlesor unfavorable fraction of slime. The discharge from this classifier isoversize which returns to the mill for regrinding, so if this dischargeshould include any appreciable quantity of the unfavorable fraction ofslime or of critical sized fines the aim of this invention tends to .bedefeated, for one feature of the invention is the keeping out of themill those larger sizes of slime solids which I have found to preventeificient grinding.

The increased density of the classifier bath also serves as adeterminant for the critical mesh or sized fines which are usuallyuncertain just which way to go-to discharge or to overflow. Theincreased density determines for them that they are to go to overflowand'away from the discharge end of the classifier; So by increasing thedensity of the classifier bath I have found that improved selectivity ofthe classifier is ob-' tainedand it canbe depended upon that most of thecritical mesh sizes will be kept out of the oversize sand discharge.

Imay also control the selectivity of this classifier bysupplying to theclassifier a certain volume weir. This increased volume of slime feed,and the increased volume of overflow causes a dispersion of the criticalmesh sizes in the classifier which makes for cleaner classification.Thus I contend that in a classifier, I can improve the selectivity ofclassification by increasing the density of the classifying mediumcoupled with an increase of volume of fluid fed thereto, and an increaseof velocity of overflow. In this particular instance, an increase ofvolume of fiuid fed the classifier also produces increased velocity ofoverflow, but I can conceive of circumstances where other means thanincreased volume of fluid feed is necessary to increase the velocity ofoverflow. That is, I propose to improve classification or selectivity ofclassifier x by doing three things, namely, circulating slimy fluid tothe classifier to increase the volume of fluid passing therethrough;'increasing the velocity of overflow over the end weir which may also bea submerged weir; and increasing the density of the classifying medium.While increasing the density of the classifying medium, I may, byrecirculating slime, increase the dilution of the classifier overflow,since'the slime recirculated will normally have a higher dilution thanthe classifier overflow, as they form a selected portion of the overflowsolids together with amajor portion of the water and have a densitylower than the primary classifier overflow. At the same time the ratioof slimes to water in, the primary classifier overflow is maintainedrelatively-the same if not increased.

The density, the volume of fluid fed, and the velocity of overflow mustbe carefully controlled for the particular material being treated sothat the density will be high enough to cause the as-' v sured overflowof the critical sizes of fines but place in a secondary classifier Y.Here classi--v fication takes place but the operation of this classifieris controlled so that the finished fines are discharged and so are theunfavorable fraction of slime solids. That is, this secondary classifierY, or any equivalent thereof which maybe used, is depended upon toselect out and to overflow the favorable fraction of the slime solidsfrom the unfavorable fraction and the fines. The dependability of thisseparation or selection is important to' the successful carrying out ofthis invention. So to be doublysure that the selection of the favorablefraction of slime solids will be carefully accomplished, wash water isapplied" to the secondary classifier Y, as indicated on the 'flowsheetshown in Fig. 1. This sheet of wash. water serves as a screen forholding back away from the discharge end. the favorable fraction ofsmaller slime solids. This assures their going out the classifieroverflow and not becoming lost to the circuit by going out the dischargeendalong with the fines and the unfavorable larger slime solids. Thisclassification and wash water also assure the unfavorable slime solidssettling out whereby they are prevented from getting into the overflowand thus back into the circuit where they are so harmful. This washwater also has 1:1. Thus the end product is un circuit but as the amountn d lated with the new miilff i the added function of restoringto thecircuit, the

water which passes from it throu g li the' secondary classifierdischarge with the fiiiislied oduct. In one mill circuit the finishedi'oductfrom the secondary classifier had a su den 50% or ""11 Thisprecise amount of water has to stant, it is a simple matter t--th"new-water being fed to the circuit,f;for-

' erely 'corthe finished product to have lution, the ratio of newwaterto n H should be varied accordinglyjp- Reference has been madam t e'con'stant 'density of the recirculatedslimeand to the constant dilutionof the sand dischafge; both flowingfrom the secondary classification'stag or classifier.

This is accomplished' by'thesetting up in that classifier of aconditionhf automatic-balance. We have at thefo'verflo'wj' end ofthe'fclassifler'a zone of greater'fdensityIthan in the zone at thedischarge end, 'f'ihis is because of the wash water, which beingfappliedsubstantially at the zone of emergence of ,the"'jclassifier blades,"keeps the fines and slime washed back away "from that zone,whereupon'the zone of' emergenceof the blades becomes azonefof greaterdilution".- As the wash water washesbackthe slime' and'fines intothe'overfiow end of the classifien their concentration at that end setsup therein and -there at, a zone of increased density which ismaterially greater than the density of the zone of dilution orrake-blade emergence.

In Fig. 2 classifier Y is shown more or less. diagramrnatically in whichI I indicates the inclined bottom or deck of the classifier, l2 theoverflow end, I! the, submerged-weir, Q the discharge end, andiitheraking' blades; or other mechanism. The submerged weir I3 dividesthe classifier tank'into two hydraulically communicable compartments orsections, in one of which the raking blades Iiope'rate. The classifieroverflows into the other compartment or section Z, in

which the favorable fraction"of slime fiows and accumulates, and fromwhich it is withdrawn through outlet pipe 16 controlled by a suitablevalve l7. l8 indicates the zone of emergence of the raking blades 15which is also the zone of dilution, while l9is the zone of increaseddensity. The wash water is addedat". The-normal horizontal liquid levelfor the classifier is indicated in full lines at 2l, while the actualliquid level line assumed by the classifier bath, under balancedconditions is indicated by the dotted line 22. As the density in thedense zone 19 is built'up, it naturally takes more dilute liquid in thedilute zone '18 to balance it. In order'to get enough of the dilutemixture in the zone 18 to balance the dense zone, the liquid level'ofthe dilute zone. rises and produces a 'superelevation.

In effect, it is as if the classifier were a U-tube with the denser zonein one arm' of the tube and the dilutezone in the other. Under theseconditions, it can bevisualized that the liquid in the dilutearmwillbehl'gher than the dense liquid in the otherarm, if the liquid in thetwo arms is to be in'balance; This isexactlyf what happens in thisclassifier, so the liquid level in the dilute zone l8 isautomaticallymaintained higher than in the dense zone '19, for they thus balance eachother. Under voperatingconditions, of

course, with the incoming wash water-there is a tendency for the liquidlevel in the dilute zone I! to build up highe'rthan is necessary tobalance i the dense zone 19, and when this happens, the [excess waterpasses out of the discharge end ll able place in the circuit.

of the'classifier along because the classifier charge end intersects theplane of the balanced liquid level 22. But at the same time, this slightrising of the liquid level in the dilute zone reacts to raise somewhatthe liquid level in the dense zone, and this slight rising thereof,causes an overflow over the weir i3 of enough slime to bring the liquidlevels back into balance. Thus there goes on a constant building up ofthe level in the dilute zone which acts partly'to discharge some of thewash water with the raked product, and partly to raise the liquid levelin the dense zone whereby there is produced an overflow of the slime.However, one zone balances the other, so the two zones quickly,constantly, and auto matically return to equilibrium. It is thisautomatically balancing condition within this classifier that causes thewithdrawn slime tobe of constant density. As has been stated, the slimewithdrawn from this classifier constitutes the favorable fractionthereof which is circulated through the circuit, while the emergeddischarge from this classifier constitutes the unfavorable fraction oflarger slime solids and the fines, both of which form the finishedproduct of the circuit. The selected favorable fraction of slimeoverflowing the weir of classifier Y is collected in some suitablecontainer such as compartment Z from whence it is fed back to the millor other desir- The liquid level in the compartment Z is the same asthat in the back end of the classifier adjacent to or abuttingcompartment Z and the weir i3 is submerged. This is necessary if, forany reason, an increased with the raked product,

amount of liquid is withdrawn from compart ment Z, the entire liquidlevel of the classifier drops momentarily and then all of the wash wateris promptly retained until the liquid volume is restored and balance isagain attained. In my preferred form of arrangement, some of thefavorable fraction goes to the mill and some to the classifier X as hasbeen explained above.

Operation-In order to make the operation of this invention clear, let usassume a new closed circuit mill has been constructed and is ready to bestarted up. The operator will load up his mill and start it going alongwith the classifiers X and Y. However, his first object will be to buildup in the circuit an ample supply of favorable fraction of slime. Thiscould be done eithenby adding or introducing slime withappropriatecharacteristies to the circuit, or, by directing all of thewater being added to the circuit to flow thereto through the wash waterpipe 20.

As soon as an inspection tells'the operator that there is enoughfavorable fraction of slime in the I circuit to give him his desiredmill efficiencies,

and he observes that his classifier Y has reached a balanced condition,then he cuts down on the amount of wash water being fed to classifier Yand by-passes the remainder of the new water re-- quired by the circuit(to make up for the water losses going out with the raked end product)so that it is led to classifier X, and preferably mixed with the slimefeed thereto. The regulation of the amount of wash-water being fed toclassifier Y is the one important adjustment in the whole system forotherwise all of the conditions appear to be automatically adjustable.He watches his is so levelled that the disfeed water to make sure it isjust enough to keep the classifier Y in operating balance. If he doesthis, the density of the discharge product from classifier Y containsthe fines plus the undesirable or unfavorable fraction of slime solidsand its dilution is constant at whatever is wanted, such as 1:1. Thisalso gives him the favorable fraction ofslime withdrawable from theclassifier containing a minimum of unfavorable sized slime or fines andalso assures him ofa constant density of the favorable fraction ofslime. This favorable fraction of slime is circulated to the mill, tothe classifier x, or to both, as may be found to give the best millingconditions wherein the grains stick to and coat the grinding media, andthe grinding media and the mass being ground are freely mobile withrespect to each other. In other words, to produce the conditions in themill of what I have termed herein Plastolubricity.

He also checks the overflow from classifier X to make sure thatconditions therein are correct. That is, to see that its bath is denseenough to assure proper selectivity thereof, as well as the volume ofinfiowing or infeeding slime thereto and also the velocity of overflow,for it is imperative that a maximum of critical mesh sizes and fines arekept in the overflow. If this classifier is not classifying to thedegree required, he brings it to proper functioning usually by feeding agreater quantity of the favorable fraction of slime from the classifierY overflow (or compartment Z) until conditions are right. If too muchslime is being discharged with the raked oversize in classifier X, hewill cut down on the quantity of favorable fraction of slime being fedto the classifier until the slime and fines are being properlyoverflowed by this classifier X. And that, along with any desirablevariation in rake speed, is about all the operator needs to do for oncethe circuit is functioning well, it tends to continue to do so with verylittle attention. The circulating load seems to take care of itself andautomatically adjusts itself to anyvariation in the ore being ground.

I claim:

1. Classification apparatus comprising a tank having a sloping bottomdeck providirm a bath space having a deep end, raking mechanism forconveying solids settled on said deck to emerged discharge, a feedsupply of pulp to be treated, an outlet for suspended slimes from saiddeep end, a weir between the slimes outlet and the emerged dischargedisposed to divide said bath space into two sections, an agitated and aquiescent one, in one of which operates said raking mechanism, the otherone of which includes said deep end and said suspended slimes outlet,control means for said slimes outlet arranged and adapted to insureconstant hydraulic communication of the liquid bodies in both saidsections across said weir which ARTHUR JOHN WEINIG.

